The present invention relates to a novel siloxane containing monomer, novel copolymers of that monomer, and the use of such copolymers in making contact lenses having high oxygen permeability.
Typical examples of known contact lenses developed with the object for continuous wear for a long term are silicone rubber contact lenses prepared from polydimethyl siloxane as a main component and high water content contact lenses prepared from poly-N-vinylpyrrolidone as a main component.
Since the silicone rubber contact lenses are very water-repellent and greatly different from cornea in thermal properties such as thermal conductivity and thermal diffusivity, they give a foreign body sensation, particularly a burning sensation despite having a large oxygen permeability. Therefore, there is required a strong patience to accommodate to the silicone rubber lenses. Further, the silicone rubber is so soft and elastic that they are subjected to precise mechanical treatments such as cutting, grinding, and polishing with difficulty. Also, many attempts for making the surface of silicone rubber lenses hydrophilic have been undertaken, but no completely satisfactory contact lens has been developed.
Since the high water content contact lenses contain about 60% to about 80% by weight of water, they have the disadvantages that (1) they are weaker in quality of material then low water content contact lenses, (2) they are easily contaminated with inorganic and organic compounds in tears which penetrate and accomulate into the lenses during the use, and (3) they are bad in maintenance of lens contour due to the evaporation of water during the use and, therefore, the refractive power thereof easily changes.
The most common soft contact lenses are prepared from poly(2-hydroxyethyl methacrylate) as a main component. In general, the water content of these contact lenses is usually of the order of 40% by weight and the oxygen permeability is insufficient. Therefore, these contact lenses have the defect that they cannot be worn continuously for as long a time as desired.